Details

Problem Description

When verifying a PKCS#1 v1.5 signature, OpenSSL ignores any
bytes which follow the cryptographic hash being signed. In
a valid signature there will be no such bytes.

Impact

OpenSSL will incorrectly report some invalid signatures as
valid. When an RSA public exponent of 3 is used, or more
generally when a small public exponent is used with a
relatively large modulus (e.g., a public exponent of 17 with
a 4096-bit modulus), an attacker can construct a signature
which OpenSSL will accept as a valid PKCS#1 v1.5 signature.